The present invention concerns a microwave dielectric ceramic composition and, more in particular, it relates to a microwave dielectric ceramic composition having a temperature coefficient of a resonance frequency (hereinafter simply referred to as .tau.f) varied generally within a practical characteristic range while maintaining a practical unload Q (hereinafter simply referred to Qu) and a greatly improved specific dielectric constant (hereinafter simply referred to as .epsilon.r).
The present invention also concerns a microwave dielectric ceramic composition in which each of the characteristic is balanced at a practical level.
The present invention further concerns a microwave dielectric ceramic composition in which .epsilon.r and Qu are controlled generally within a practical characteristic range while maintaining .tau.f at a practical high level and each of the characteristics is balanced at a high level.
The present invention further concerns a microwave dielectric ceramic composition in which .epsilon.r, Qu and .tau.f are controlled generally within a practical characteristic range and each of the characteristics is maintained in a well balanced state.
The present invention is utilized for impedance matching or the like of dielectric resonators, microwave integrated circuit substrate, various kinds of microwave circuits in a microwave region and it is particularly suitable to LC filter materials.
Generally, LC filter materials, dielectric resonators, dielectric substrates used in a region of high frequency waves such as microwaves or milliwaves are required to have high .epsilon.r and high flu, as well as small absolute value for the temperature coefficient of the resonance frequency.
Namely, since the dielectric loss of a microwave dielectric ceramic composition (hereinafter simply referred to as dielectric ceramic composition) tends to increase as the working frequency becomes higher, a dielectric ceramic composition having large .epsilon.r and Qu in a microwave region is desired.
For such a dielectric ceramic composition, a composition belonging to a composite perovskite structure such as Ba(Zn.sub.1/3 Ta.sub.2/3)O.sub.3 or Ba(Mg.sub.1/3 Ta.sub.2/3)O.sub.3 or BaO--TiO.sub.2 system composition has been used in recent years, but any of them requires a high sintering temperature of 1300.degree. C. or higher.
Such a high sintering temperature requires greater power electric power consumption during sintering to result in a drawback of causing a disadvantage in view of production cost or productivity.
Further, in a case of sintering together with a conductor having a low melting point as an electrode, for example, silver (melting point: 961.degree. C.) or copper (melting point: 1083.degree. C.) as in an LC filter or a strip line filter, it is particularly advantageous that the sintering temperature is lower than the melting point of the conductor. Accordingly, a material sinterable at a temperature as low as possible is demanded.